Generally, at a time of curing the tire, the molding surface of the tire forming mold is pressed against the tread surface, and the tread pattern corresponding to a concavo-convex shape of the molding surface is formed. At this time, air existing between the tread surface and the molding surface is compressed into the depression for forming the land portion, however, if the curing is carried out with the air left, there is a problem that a concave chip called as lightness is generated in the tread surface and a defective molding is generated. Accordingly, it is important to suitably discharge the air compressed into the depression out of the mold.
As a lightness countermeasure, it is general to employ a method of piercing a vent hole communicating with an outer side of the mold in the depression, thereby discharging the air. However, since a lot of rubber projections called spew are formed in the tread surface, an ablating work is necessary and there is a problem that the dropout spew is mixed as a foreign material into the mold, which results in a defect. On the contrary, there has been proposed a tire forming mold structured such as to embed a laminated blade obtained by superposing a plurality of thin plates in the depression and the air is discharged through a micro gap (for example, the following patent documents 1 and 2). The micro gap mentioned above is set such that it passes the air therethrough and does not pass a heated and softened rubber therethrough with a viscosity difference.
However, in the case of using the laminated blade in which one end portion is exposed to the molding surface and the other end portion is exposed to a mold back face, such as the following patent document 1, since a tire diametrical distance in which the air moves within the micro gap becomes long and air resistance is increased, an air discharging effect may be obstructed, and thus there is room for further improving this. On the other hand, if the gap of the laminated blade is enlarged in order to improve this, the rubber makes an intrusion into the gap, so that the same problem as that in a case where the vent hole is provided is generated.
Further, in the case of using a laminated blade in which a side end is exposed to the molding surface and an end portion is exposed to a mold split surface (for example, a split surface between segments) such as the following patent document 2, there is a tendency that it becomes hard to discharge the air in a place which is away from the mold split surface, and there is a defect that the air discharging effect depends on an arranged position of the laminated blade. Further, since the laminated blade is directly embedded in the depression in both the following patent documents, a work for setting and regulating the micro gap is complicated.
Patent Document 1: Japanese Unexamined Patent Publication No. 4-338512
Patent Document 2: Japanese Patent No. 3541261